The April 2014 report became public last year as tribes raised concerns about the damage caused to the monument. Pits were dug throughout the site, intrusive walkways were constructed and a former superintendent even admitted that he removed ancestral remains and kept them in a box in his garage.

"It was kind of a stomach-turning anger and disappointment," Johnathan Buffalo,
the historic preservation director for the Meskwaki Tribe, told The Sioux City Journal in May 2014.

"He thought he was protecting something. He didn't see us as human beings," Buffalo added. "He just saw a science project."

The group, however, kept a copy of the report, which included a section that detailed a visit by tribes to the monument. They were shocked by what they saw in December 2009.

"Tribal representatives were fairly angry about the boardwalks and one even asked why ancient cemeteries should be treated as places to walk your dog," a NPS memo stated.

As for the remains that were kept by former superintendent Tom Munson, they are being returned to tribes under the Native American Graves Protection and Repatriation Act. Buffalo told The Sioux City Journal that he believes Munson took them home to prevent their reburial.

The paper reported at the time that Munson was under federal investigation for taking the remains home. It's not clear if he will ever face punishment.

"Created 65 years ago, this little park is supposed to preserve sacred sites, not serve as a construction playground for clueless and criminal federal employees," Timothy Mason, who used to work at the monument and is now a part of a group called Friends of Effigy Mounds, said in a press release.